Wireless networks have experienced increased development in the past decade. Two types of wireless networks are infrastructure-based wireless networks, and ad hoc wireless networks.
An infrastructure-based wireless network typically includes a communication network with fixed and wired gateways. Many infrastructure-based wireless networks employ a mobile unit which communicates with a fixed base station that is coupled to a wired network. The mobile unit can move geographically while it is communicating over a wireless link to the base station. When the mobile unit moves out of range of one base station, it may connect or “handover” to a new base station and starts communicating with the wired network through the new base station.
In comparison to infrastructure-based wireless networks, such as cellular networks or satellite networks, ad hoc networks are self-forming networks which can operate in the absence of any fixed infrastructure, and in some cases the ad hoc network is formed entirely of mobile nodes. An ad hoc network typically includes a number of geographically-distributed, potentially mobile units, sometimes referred to as “nodes,” which are wirelessly connected to each other by one or more links (e.g., radio frequency communication channels). The nodes can communicate with each other over a wireless media without the support of an infrastructure-based or wired network. Ad hoc networks can also be self-healing. Links or connections between these nodes can change dynamically in an arbitrary manner as existing nodes move within the ad hoc network, as new nodes join or enter the ad hoc network, or as existing nodes leave or exit the ad hoc network. Because the topology of an ad hoc network can change significantly techniques are needed which can allow the ad hoc network to dynamically adjust to these changes. Due to the lack of a central controller, many network-controlling functions can be distributed among the nodes such that the nodes can self-organize and reconfigure in response to topology changes.
One characteristic of the nodes is that their transmission range is usually relatively limited in comparison to cellular networks. Each node can typically directly communicate over a short range with nodes which are a single “hop” away. Such nodes are sometimes referred to as “neighbor nodes.” When a node transmits packets to a destination node and the nodes are separated by more than one hop (e.g., the distance between two nodes exceeds the radio transmission range of the nodes, or a physical barrier is present between the nodes), the packets can be relayed via intermediate nodes (“hop-by-hop”) until the packets reach the destination node. Each intermediate node acts as a router which can intelligently route the packets (e.g., data and control information) to another node until the packets eventually reach their final destination. To assist with relaying of packets, each node may maintain routes or routing information to other nodes in the network and can utilize routing techniques to adapt to changes in the interconnectivity between nodes. The nodes can maintain this routing information by performing periodic link and topology updates. Alternatively, nodes may discover routing information only when needed, instead of utilizing updates to maintain routes.
As can be appreciated from the dynamic nature of wireless ad-hoc networks such as those discussed above, the neighborhood topology of a particular node can change rapidly over time. One approach to detect mobility amongst nodes in a network is to employ active time-of-flight measurements. This method entails performing active measurements on the time-of-flight (or transmission time) between a particular node and a stationary device. The rate of change of the time-of-flight value determines the mobility of the particular node. This method, however, requires the sending of special “time-of-flight” messages to the stationary devices, which requires repetitive and extraneous measurements and comparisons. Moreover, this method fails to account for situations where a node moves in a substantially elliptical or circular manner around a particular fixed node. In these situations the “time-of-flight measurements” will be approximately the same value and, hence, the node will incorrectly assume itself to be stationary. Moreover, time-of-flight measurements also consume a significant number of CPU cycles to do accurate time measurements and comparisons and thus consume battery power.
Another approach for detecting mobility amongst nodes in a network is to employ signal strength measurements. Mobility of particular nodes can be estimated by the rate of change of signal power from a particular stationary node. This method, however, fails to account for RF interference from neighboring nodes and can therefore lead to inaccuracies.
Notwithstanding these advances, it would be desirable to provide improved techniques for determining whether a node in a wireless communication network, such as, an ad-hoc peer-to-peer multi-hop network or a mesh network, is mobile or stationary. It would also be desirable if such techniques consumed less computing resources, power and bandwidth.
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